已知角a为锐角,sin(A+15°)=4/5,则cos(2A-15°)=

角A为锐角,sin(A+15°)=4/5,∴cosA=cos[(A+15°)-15°]=cos(A+15°)cos15°+sin(A+15°)sin15°>0,∴cos(A+15°)=3/5,∴sin2(A+15°)=24/25,cos2(A+15°)=1-2[sin(A+15°)]^2=1-32/25=-7/25,∴cos(2A-15°）=cos[2(A...